1. Field of the Invention
The present invention relates to a hydraulic circuit including a first system having a changing valve for a right side running motor and a changing valve for a first actuator to be connected to a first pump and a second system having a changing valve for a left side running motor and a changing valve for a second actuator to be connected to a second pump.
2. Description of the Related Art
Conventionally, as a hydraulic circuit of a construction machine, a hydraulic circuit a hydraulic circuit including a first system having a changing valve for a right side running motor and a changing valve for a first actuator to be connected to a first pump and a second system having a changing valve for a left side running motor and a changing valve for a second actuator to be connected to a second pump has been known (refer to Patent document 1). In the hydraulic circuit described in this patent document 1, a merging valve (15) for communicating and interrupting a discharge path (13a) of a first hydraulic pump (13) and a discharge path (14a) of a second hydraulic pump (14) and a changing valve (16) for selectively supplying the discharge path (13a) and the discharge path (14a) to one among a first circuit (17) and a second circuit (18), respectively.
[Patent document 1] JP-A-10-252105
However, in the hydraulic circuit configured as described in the patent document 1, when the merging valve (15) is located at an interruption position (b) and further, a changing valve (16) is located at a second position (d) in order to secure the independent state of a running system in the combined control of hydraulic motors for right and left running (5, 7) and the other actuator, hydraulic oil to be supplied from the second hydraulic pump (14) is only supplied to the hydraulic motors for right and left running (5, 7). Therefore, this involves a problem such that the amount of the hydraulic oil to be supplied to the hydraulic motors for right and left running (5, 7) runs short and a running speed is limited. In addition, since the merging valve (15) and the changing valve (16) are provided, as shown in FIG. 2 of Patent document 1, two valves are needed and this makes the hydraulic circuit larger or as shown in FIG. 3 of Patent document 1, it is necessary to provide a double structure spool and this makes the hydraulic circuit into a complex mechanism.